[en] Measurement has been made about the time rate of the attachment of low energy electrons to O₂ molecules in Ar-N₂-O₂ gas mixture with a pulse ionization chamber and a pulse-height analyzer. The reduced rate, which means the observed attachment rate divided by O₂ pressure, increased roughly linearly with increasing Ar pressure, but soon passed a maximum which was followed by a broad minimum. After the minimum, the curve began to rise slowly, and approached a straight line with moderate slope. Attempt was made to explain these features in terms of the change of electron energy distribution with the mixing ratio of component gases at some fixed average electron energy. The well-known Block = Bradbury mechanism of two-stage three-body attachment may operate in the present case, and the initial capture process proceeds via the lowest accessible resonance alone. The attachment rate in the present ternary mixture is given by linear combination of n(x).sigma(x).v(x) multiplied by a product of the rate of initial electron capture and the life-time of vibrationally excited negative oxygen ions. Here, the n(x) denotes the number of X molecules or atoms present per unit volume, sigma(x) the cross section for the stabilizing collision of an X molecule or atom with a negative oxygen ion, and v(x) the relative velocity of an X molecule or atom to a negative oxygen ion. Discussions concerning the present experimental results are given according to the above mentioned relation. (Kato, T.)